A climate control system on a vehicle, such as a motor vehicle, maintains a condition within an occupant compartment of the vehicle at a comfortable level by providing heating, cooling and ventilation. One example of a condition is air temperature, another is air distribution, while still another is air flow rate. Typically, the comfort level is subjectively determined by an occupant of the vehicle and communicated to the climate control system via a set point or other temperature control actuator, as is known in the art.
Climate control within the occupant is maintained by an integrated mechanism referred to in the art as a heating, ventilation and air conditioning (HVAC) system. In an automatic HVAC system, the comfort level within the occupant compartment of the vehicle is dependent on many objective and subjective factors, such as occupant preference, vehicle operating conditions, ambient temperature, humidity level, and sun heating load. The HVAC control system typically includes sensing mechanisms either within or outside the occupant compartment to maintain the desired comfort level. One example of a sensing mechanism is an ambient temperature sensor that measures the outside air temperature. The outside air temperature sensed by the ambient temperature sensor is one of several factors used by the HVAC system in maintaining the comfort level within the occupant compartment.
An ambient temperature sensor is typically located behind the vehicle front bumper. The sensor reading sometimes is increased by the engine heat, or the ground heat while the vehicle is idling, short time parking or moving at a very low vehicle speed. This causes an error in ambient temperature measurement. Typically a software routine is designed to filter out the errors in ambient temperature measurement by determining when to use the sensor reading as the control input and when to replace the sensor reading by using a previous sensor reading. The integrity of the ambient temperature sensor reading filter routine will affect the HVAC comfort level.
The key for a good ambient temperature reading is timing. The first decision needed is to determine when to stop using the sensor reading; this state is called the Heat Soak Mode. The Heat Soak Mode is typically entered when the vehicle speed is under a predetermined speed limit for a predetermined amount of time. While the system is in the Heat Soak Mode, the sensor reading is at error and will not be used. Instead the last ambient temperature sensor reading before entering the Heat Soak Mode will be used as the ambient temperature input until the system exits the Heat Soak Mode. Thus, the second decision needed is to determine when the ambient temperature sensor reading can be used again. The known prior art exits the Heat Soak Mode and uses the actual ambient temperature sensor reading when the vehicle speed is above a fixed limit for a predetermined amount of time, as disclosed in U.S. Pat. No. 5,416,728. However, the actual time period for when the ambient temperature sensor readings should be used is not fixed, but rather variable. Thus, using a variable timer will improve the accuracy of the measurement.
It is, therefore, an object of the present invention to provide, in a vehicle, a method and system for determining when to use a current ambient temperature with a climate control system after entering a heat soak mode.